1. Field of the Invention
The present invention relates to a paper discharging apparatus for a printer that transfers sheets of paper from an image printer to a plurality of paper discharging trays.
2. Description of the Related Art
In general, a printer such as a laser printer or a copier, as shown in FIG. 1, includes an image forming unit 3 for forming an image on a photoreceptor belt 2 and printing the formed image on a sheet of paper P. The paper P having a printed image is discharged to the outside of a printer body 1 by a paper discharging apparatus.
The paper discharging apparatus includes a plurality of discharge trays 4 installed in the exterior side of the printer body 1, and a transfer means for selectively transferring the paper P from the image forming unit 3 to the discharge trays 4.
The paper P is selectively discharged to one of the plurality of discharge trays 4 according to the printed image. For example, in the case where an identical image is printed onto a plurality of sheets, the sheets of printed paper are transferred to the respective discharge trays 4 to then be sorted.
The transfer means includes a pair of pulleys 5 rotatably installed in the upper and lower portions of the printer body 1, a belt 6 supported by the pulleys 5, a stepping motor 8 for driving the pulleys 5, and an indexer 7 installed on the belt 6, for clamping paper P printed and transferred. The indexer 7 is constituted by a pair of rollers 7a which rotate in contact with each other, and a motor 7b for rotating the rollers 7a. 
In the above-described configuration, the paper P printed in the image forming unit 3 is guided by a guide 9, and then clamped between rollers 7a of the indexer 7. As the belt 6 travels, the indexer 7 elevates to reach a selected discharge tray 4 as shown in phantom in FIG. 1. Then, the paper P is discharged to the selected discharge tray 4 by rotation of the rollers 7a. 
Although such conventional devices are generally thought to be acceptably, they are not without shortcomings. In particular, paper discharge occurs at a rapid rate, and therefore the indexer 7 cannot properly clamp a subsequent sheet of paper. This phenomenon is especially problematic when paper is discharged to the lowermost discharge tray 4 because the movement speed of the indexer 7 cannot catch up with the paper discharge speed from the guide 9.
An object of the present invention is to provide an improved paper discharging apparatus for a printer, which rapidly transfers successively discharged sheets of paper to discharge trays.
Accordingly, to achieve the above objective, a paper discharging apparatus for a printer includes a movement path having a first movement track and a second movement track for independently guiding paper printed in an image forming unit in a printer body. A means is provided for branching the movement path and allowing the printed paper to selectively enter the first or second movement track. A first indexer is elevatably installed in the printer body, for clamping a first sheet of paper that has passed through the first movement track and moving to a first selected discharge tray to discharge the paper thereto. A second indexer is elevatably installed in the printer body, for clamping a second sheet of paper that has passed through the second movement track and moving to a next selected discharge tray to discharge the paper thereto. A means is provided for elevating the first and second indexers, and a controller controls the driving of the elevating means and the first and second indexers.
Each of the elevating means preferably includes a pair of belts for supporting the corresponding indexer, pulleys installed in the upper and lower portions of the printer body to support the belts, and a stepping motor for rotating the pulleys.
The first indexer may include first brackets fixed on the belts, a pair of first clamping rollers rotatably mounted on the first brackets, for clamping the first sheet of paper and discharging the clamped paper to the first discharge tray, a first guide plate installed in the first brackets, for guiding the first sheet of paper discharged by the first clamping roller to the first discharge tray, and a first motor for driving the first clamping rollers.
The second indexer may include second brackets fixed on the belts, a pair of second clamping rollers rotatably mounted on the second brackets, for clamping the second sheet of paper and discharging the clamped paper to the second discharge tray, a second guide plate slidably installed in the second brackets so as to extend and retract toward and away from the discharge trays, for guiding the paper discharged from the second clamping rollers to the second discharge tray, a second motor for driving the second clamping rollers, and means for driving the second guide plate.